The proposed multicenter study to test the efficacy of providing crossmatch-negative or HLA-matched donor corneas to patients with high risk of rejection will require the services of a histocompatibility testing laboratory at each transplanting center. Each laboratory must HLA type their local patients and donors, screen local patients for preformed lymphocytotoxic antibodies, and crossmatch sera of patients from all collaborating centers against cells of local donors. In order to generate data that can be pooled for analysis, the participating laboratories must have a high degree of correlation. To achieve this degree of correlation a primary function of the Coordinating Laboratory will be to establish and monitor laboratory standards and quality control procedures, including duplicate antibody screening. In addition, the Coordinating Laboratory will receive patients' sera from all centers and distribute them on microtest trays to all laboratories for crossmatching agaist donors. The director of the Coordinating Laboratory and/or the laboratory manager will also serve as liaison between the laboratories. They will also advise the Study Chairman and Data Coordinating Center regarding analysis of histocompatibility data.